The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2001-159003 filed May 28, 2001 and Japanese Patent Application No. 2001-203916 filed Jul. 4, 2001, which are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a steering damper for a power cylinder apparatus that produces a power assist force (steering auxiliary force) by switching a flow passage change-over valve upon a steering operation of a steering wheel and activating a power cylinder, in which the steering damper serves to damp or relieve an impact when road load such as a kick back is applied to the side of the steering wheel.
2. Description of the Related Art
Generally, the hydraulic power steering apparatus according to the related art has a flow passage change-over valve for selectively connecting a pump and a tank to a left or right chamber of a power cylinder in accordance with a steering operation of the steering wheel. This flow passage change-over valve enables a pressure oil to be supplied to any one of the left and right chambers for the power cylinder in accordance with the steering operation to apply a power assist force to rotate the steering wheel.
The vehicles having such power steering apparatus with the steering damper has been well known. This steering damper acts to damp or relieve an impact when road load (so-called a kick back) is exerted from the side of front wheels due to irregularities or an obstacle on the road surface, for example, and to prevent the impact from being transmitted to the steering wheel, when a vehicle is driving.
The steering damper according to the related art is typically provided with a aperture or a variable aperture for applying a resistance to a flow of pressure oil exhausted from a chamber of the power cylinder on the return side in accordance with the movement of a piston, when road load such as kick back is exerted on the left or right cylinder passage between the flow passage change-over valve and the left or right chamber of the power cylinder. However, this aperture or variable aperture produces a flow passage resistance to the flow of pressure oil on the supply side from the pump to one chamber of the power cylinder and the flow of pressure oil on the return side from the other chamber of the power cylinder to the tank, when a positive input is made in accordance with the steering operation of the steering wheel. This results in a problem that the responsibility of the power cylinder is decreased.
Therefore, a power damper has been already proposed in which the aperture is constituted of a variable throttle valve in the left and right cylinder passages, and a check valve is provided in parallel with the variable throttle valve, so that the pressure oil can be supplied sufficiently from the pump via the flow passage change-over valve to the cylinder chamber by opening the check valve in the corresponding cylinder passage, when a positive input is made by the steering operation (Japanese Utility Model Publication No. Hei. 2-49109).
The above Japanese Utility Model discloses that the steering damper having xe2x80x9ca check valve for permitting only a flow of oil from the change-over valve to an oil chamber of a steering damper main body and a throttle check valve with an initial load for permitting only a flow of oil from the oil chamber to the change-over valve, in a circuit connecting the steering damper main body (power cylinder) and the change-over valvexe2x80x9d.
The steering damper of the related art, which is disposed on the power steering apparatus, had a problem that the steering wheel can not be returned excellently, especially at or near the neutral position, because the variable throttle valve is not opened for a small flow from the power cylinder and does not produce any flow passage for flowing back the oil to the flow passage change-over valve. Also, if the flow passage for flowing back a fluid of small flow from the power cylinder is provided, a fluid fed from the flow passage change-over valve upon the steering operation flows out before opening the check valve, not affording a preset force, resulting in a problem that the vehicle has a bad straight drive stability (response sense) while running at high speed.
Even if the check valve is structured to be applied a preset force, when the preset force is large and, for example, rapid steering is performed, the handle turns heavy suddenly or is returned unfavorably. This is a problem.
In order to avoid the problem that the steering wheel can not be returned excellently, especially at or near the neutral position, because the variable throttle valve is not opened for a small flow from the power cylinder, the steering damper according to the related art provided in the power steering apparatus is formed with a leak passage having a plurality of narrow grooves arranged at an equal interval in a circumferential direction on the valve plug side or valve seat side for the check valve (JP-A-Hei. 11-49004).
However, there was a problem with the shape of the leak passage according to the related art as described in JP-A-Hei. 11-49004 that the manufacturing costs were high, and because of the leak passage consisting of the plurality of narrow grooves, it was difficult to hold the balance on the circumference or to control the passage area at high precision.
The present invention has been achieved in the light of the aforementioned problems, and it is an object of the invention to provide a steering damper for suppressing a negative pressure occurring in the cylinder passage at the time of rapid steering or when the handle is returned, thereby avoiding a situation that the handle turns heavy suddenly or is returned unfavorably.
Also, it is another object of the invention to provide a steering damper in which the shape of the leak passage is worked at high precision and the manufacturing costs can be reduced.
Further, it is another object of this invention to provide an inexpensive steering damper in which the material costs and the working costs can be reduced.
Moreover, it is another object of this invention to provide a steering damper in which a pressure loss in a flow of the fluid passing from the inside of the valve plug for the check valve to the outside is greatly reduced to be almost equivalent to the pressure loss of a flow of the fluid passing from the outside to the inside.
Further, it is another object of the invention to provide a steering damper in which the aperture can be tuned easily by properly adjusting the length of the communication hole formed on the bottom of the second valve plug.
According to a first aspect of the present invention, there is provided a steering damper attached to a power steering apparatus having a flow passage change-over valve for selectively changing a flow passage among a pump and a tank and left and right chambers of the power cylinder in accordance with steering operation of a steering wheel, and a pair of left and right cylinder passages for connecting the flow passage change-over valve to the left and right chambers, the steering damper comprising:
a pair of damper portions each having:
a variable throttle valve for restricting inflow from the power cylinder into the flow passage change-over valve, the variable throttle valve provided between the flow passage change-over valve and each of the left and right chambers of the power cylinder; and
a first check valve for permitting inflow from the flow passage change-over valve into the power cylinder, the check valve connected in parallel with the variable throttle valve; and
second check valves in communication to the tank, provided between the first check valves and the left and right chambers.
The steering damper according to the first aspect of the invention has the second check valve in communication to the tank in each of the cylinder passages leading from the flow passage change-over valve to the left and right chambers of the power cylinder. Therefore, at the time of rapid steering, for example, if the supply of a pressure oil to one cylinder chamber is delayed to cause the cylinder passage to become a negative pressure, the second check valve is opened to communicate to the tank to refill a working fluid, thereby preventing the handle from turning heavy.
According to a second aspect of the invention, the steering damper according to the first aspect of the invention further has communication bores provided between the flow passage change-over valve and the left and right cylinder chambers. The communication bores are connected in parallel with the variable throttles, respectively.
According to a third aspect of the invention, there is provided a steering damper attached to a power steering apparatus having a flow passage change-over valve for selectively changing a flow passage among a pump and a tank and left and right chambers of the power cylinder in accordance with steering operation of a steering wheel, and a pair of left and right cylinder passages for connecting the flow passage change-over valve to the left and right chambers, the steering damper comprising:
a pair of damper portions each having:
a variable throttle valve for restricting inflow from the power cylinder into the flow passage change-over valve in accordance with steering operation of a steering wheel, the variable throttle valve provided between the flow passage change-over valve and the left and right chambers of the power cylinder; and
a first check valve for permitting inflow from the flow passage change-over valve into the power cylinder, the check valve connected in parallel with the variable throttle valve;
wherein the variable throttle valve has:
a step portion, which is a valve seat of the variable throttle valve formed on an inner surface of a housing; and
a barrel-like valve plug for abutting with the step portion to close the variable throttle valve;
wherein a first biasing member biases the barrel-like valve plug in a valve seat direction;
wherein the first check valve has:
a cylindrical valve plug with bottom for abutting an opening portion of the barrel-like portion to close the first check valve; and
a second biasing member for biasing the cylindrical valve plug with bottom from a direction opposite to the first biasing member; and
wherein a communication bore is formed through a bottom face of the cylindrical valve plug with bottom.
Since the steering damper according to the third aspect of the invention is provided with the communication bore through the bottom face of the cylindrical valve plug with bottom for the first check valve as the leak passage, the passage area can be controlled at high precision and the manufacturing costs can be reduced.
According to a fourth aspect of the invention, the steering damper according to the third aspect further has second check valves in communication to the tank. The second check valves are provided between the first check valves and the left and right chambers of the power cylinder.
According to a fifth aspect of the invention, there is provided the steering damper according to the first aspect in which a valve plug of the first check valve is molded by press working.
In the fourth and fifth aspects of the invention, the valve plug of the check valve is molded by press working, whereby the material costs and the manufacturing costs can be greatly reduced.
According to a sixth aspect of the invention, there is provided the steering damper according to the third aspect in which a valve plug of the first check valve is molded by press working.
Also, according to a seventh aspect of the invention, the cylindrical valve plug with bottom has a passage hole to penetrate inside and outside in a cylindrical portion thereof. A cap is attached within the cylindrical valve plug on a side closer to the bottom thereof than the passage hole.
According to an eighth aspect of the invention, fluid from the flow passage change-over valve is flown from an outer face of the cylindrical valve plug through the passage hole thereinto. Fluid from the side of the power cylinder is flown from the inside of the cylindrical valve plug through the passage hole to the outer face thereof.
According to a ninth aspect of the invention, the cap has an inclined face for smoothly flowing a fluid that flows from the inside of the passage hole to the outside thereof.
In the seventh to ninth aspects of the invention, since the a space on the bottom portion of the valve plug for the check valve can be eliminated or decreased by the cap, a pressure loss of fluid flowing from the inside of the valve plug to the outside is reduced.
According to a tenth aspect of the invention, a communication bore that penetrates through a bottom face of said valve plug for said check valve is formed and a communication bore is formed on a bottom face of the cap.
In the tenth aspect of the invention, the valve plug for the check valve molded by press working has so small a thickness that the length of the communication bore can not be secured sufficiently, but it is possible to secure a required length of the communication bore (aperture hole) by providing the similar communication bore in the cap.
According to a eleventh aspect of the invention, the steering damper has the cap molded by press working.
According to a twelfth aspect of the invention, the communication bore is defined by a plurality of the caps, which overlap each other.
According to a thirteenth aspect of the invention, the length of the communication bore is variable.
In the twelfth and thirteenth aspects of the invention, the plurality of caps are molded by press working and overlaid, the length of the communication bore can be arbitrarily set by changing the number of layers, whereby the aperture can be easily tuned.
According to a fourteenth aspect of the invention, there is provided a power steering apparatus comprising:
a pump for supplying oil;
a tank for receiving returned oil;
a power cylinder having left and right chambers;
a flow passage change-over valve for selectively changing a flow passage among the pump and the tank and the left and right chambers in accordance with steering operation of a steering wheel;
a steering damper having:
a pair of damper portions each including:
a variable throttle valve for restricting inflow from the power cylinder into the flow passage change-over valve, the variable throttle valve provided between the flow passage change-over valve and each of the left and right chambers of the power cylinder; and
a first check valve for permitting inflow from the flow passage change-over valve into the power cylinder, the check valve connected in parallel with the variable throttle valve; and
second check valves in communication to the tank, provided between the first check valves and the left and right chambers.
According to a fifteenth aspect of the invention, the steering damper further has communication bores provided between the flow passage change-over valve and the left and right cylinder chambers and the communication bores are connected in parallel with the variable throttles, respectively.
According to a sixteenth aspect of the invention, there is provided a power steering apparatus comprising:
a pump for supplying oil;
a tank for receiving returned oil;
a power cylinder having left and right chambers;
a flow passage change-over valve for selectively changing a flow passage among the pump and the tank and the left and right chambers in accordance with steering operation of a steering wheel;
a steering damper having:
a pair of damper portions each including:
a variable throttle valve for restricting inflow from the power cylinder into the flow passage change-over valve, the variable throttle valve provided between the flow passage change-over valve and each of the left and right chambers of the power cylinder; and
a first check valve for permitting inflow from the flow passage change-over valve into the power cylinder, the check valve connected in parallel with the variable throttle valve; and
wherein the variable throttle valve has:
a step portion, which is a valve seat of the variable throttle valve formed on an inner surface of a housing; and
a barrel-like valve plug for abutting with the step portion to close the variable throttle valve;
wherein a first biasing member biases the barrel-like valve plug in a valve seat direction;
wherein the first check valve has:
a cylindrical valve plug with bottom for abutting an opening portion of the barrel-like portion to close the first check valve; and
a second biasing member for biasing the cylindrical valve plug with bottom from a direction opposite to the first biasing member; and
wherein a communication bore is formed through a bottom face of the cylindrical valve plug with bottom.
According to a seventeenth aspect of the invention, the steering damper further has second check valves in communication to the tank the second check valves are provided between the first check valves and the left and right chambers of the power cylinder.
According to an eighteenth aspect of the invention the cylindrical valve plug with bottom has a passage hole to penetrate inside and outside in a cylindrical portion thereof a cap is attached within the cylindrical valve plug on a side closer to the bottom thereof than the passage hole.
According to a nineteenth aspect of the invention, the cap has an inclined face for smoothly flowing a fluid that flows from the inside of the passage hole to the outside thereof.
According to a twentieth aspect of the invention, a communication bore that penetrates through a bottom face of said valve plug for said check valve is formed and a communication bore is formed on a bottom face of said cap.
According to a twenty-first aspect of the invention, the communication bore is defined by a plurality of the caps, which overlap each other.